There are basically two kinds of incense on the market today. One is a block of incense which may have a variety of bases such as charcoal or sandalwood, and a variety of shapes such as conical, frustoconical, pyramidal, rectangular, parallelepiped, and others. The incense block is lit and placed in an ashtray for example. As the incense burns, it emits a fragrance. A second basic kind of incense currently available comes in stick form. It has a long stick most of which is covered with a layer of incense material. The unlayered portion of the stick may be held or placed in the ground, for example, while the other end is lit. Again the burning incense emits a fragrance.
With either product, the burning time is fixed. However long it takes the block to burn out or however long it takes the incense stick to burn out is how long the incense will burn. Once lit, it is difficult to extinguish it without destroying its future usefulness. For example, the burning incense could be extinguished by dousing it with water. Obviously, however, it could not be used again.
In certain instances, it would be desirable to have incense which can continuously emit a fragrance for a long period of time, say an hour, without having to light additional pieces of incense. On other occasions, it might be desirable to have a very short burning time.